The objective of this study is to elucidate the biological role of cyclic GMP (cGMP) in the regulation of function of human neutrophils and bovine coronary arterial smooth muscle. Past studies suggested that cGMP was associated with and perhaps mediated several neutrophil functions (secretion, phagocytosis, adherence) and vascular smooth muscle contraction. These conclusions were based on the observations that immune reactants, calcium ionophores and acetylcholine elevated cGMP levels in neutrophils and concomitantly stimulated secretion and phagocytosis. Likewise, acetylcholine and tissue hormones elevated cyclic GMP levels in vascular smooth muscle and elicited contraction. However, recent studies in this laboratory have indicated that nitric oxide and nitroso compounds such as the vasodilator nitroprusside and the carcinogen nitrosoguanidine markedly elevate tissue cGMP levels, activate guanylate cyclase and relax smooth muscle. Similarly, nitroso compounds elevate neutrophil cGMP levels but do not elicit secretion or phagocytosis. Further, these effects of nitroso compounds are not dependent on addition of calcium. Preliminary data indicate that in the presence of immune reactants neutrophil function can be inhibited by nitroso compounds at a time when cGMP levels are markedly elevated. Thus, contrary to what was believed previously, cGMP may not be the important signal for initiating or stimulating neutrophil function. The proposed study will focus attention on the precise relationships between cGMP levels and neutrophil function in the presence of various immune reactants and calcium. Neutrophil guanylate cyclase will be purified and characterized with respect to activation by nitroso compounds and calcium. Chemical agents which we have determined to interfere with intracellular mechanisms of cGMP accumulation (vital biological electrophilic stains, cytochalasin A) will be tested for their effects on neutrophil function and guanylate cyclase activity. These studies should provide greater insight to the relationships between cGMP accumulation and neutrophil function.